PROJECT SUMMARY Neuropsychiatric disorders (NPD), such as schizophrenia, bipolar disorder, and autism are behaviorally-defined and etiologically-heterogeneous conditions with a wide range of severity and outcomes. For cancer and other common diseases, the study of rare genetic disorders has illuminated key pathophysiological mechanisms, resulting in significant treatment advances. We hypothesize that this strategy can be successfully applied to NPD. New genomic technologies have led to the discovery of hundreds of rare genetic NPD due to copy number (CNVs) and single gene nucleotide variants (SNVs) of large effect size. However, detailed neuropsychiatric profiles have not been established for most of these conditions, due in part to difficulty recruiting adequate cohort sizes to power statistical analyses. We will capitalize on large NPD clinical populations at Geisinger, the University of Washington, and Washington University in St. Louis to recruit individuals with rare genetic disorders for this study. We will also examine the influence of additional contributors throughout the genome to the variable expressivity of neuropsychiatric symptoms in these disorders. This study will systematically examine these aspects of rare genetic NPD through the following aims: 1) Employ a highly cost-effective, genetics-first strategy to achieve baseline characterization of a large cohort with genetic NPD etiologies. Every year, as part of psychiatric, developmental, and behavioral healthcare, valuable genotype and phenotype data are generated from individuals with rare genetic NPD. We will harmonize core assessment batteries used in clinical care to leverage this high-quality data for broad data sharing and analyses on >1,000 probands, accelerating discovery and greatly reducing the research cost of multidimensional phenotyping. 2) Describe detailed phenotypic signatures in selected rare genetic NPD, including the impact of family background on variable expressivity. We will characterize quantitative neuropsychiatric traits for selected rare genetic NPD (initially 1q21.1 and 15q13.3 CNVs and CHD8 SNVs). All three disorders have shown genome-wide significance for increased risk of neuropsychiatric phenotypes, including psychosis, mood disorders, and autism. We will assess behavioral, psychiatric, and cognitive traits in 250 probands with these rare genetic NPD and their first- degree family members to explore the impact of family background on variable expressivity of neuropsychiatric symptoms. 3) Assess the contributions of common and secondary rare genomic variants to variable expressivity in rare genetic NPD. Through two sub-aims, we will explore the impact of common (polygenic risk scores) and rare (`second hits') genomic contributors on risk or resilience for neuropsychiatric symptoms. Analyzing data collected through Aims 1 and 2, in addition to a broader exploration of genomic and electronic health record data from 250,000 individuals in Geisinger's MyCode cohort, we will demonstrate how different genomic background contributors lead to clinical heterogeneity in individuals with rare genetic NPD. These studies may eventually inform individual-level prognoses for neuropsychiatric outcomes.